Question

我尝试做一个具有扩展方法的自定义类，但遇到编译时错误。我把它放在我的.h文件中：

class Byte
{
    public:
        Byte();
        ~Byte();
        std::string  DataType;
        int  ColumnWidth;
        std::vector<unsigned char> data;
        int ToLittleEndianInt() {
            long int Int = 0;
            int arraySize = this->ColumnWidth;
            if (arraySize == 2)
            {
                Int = this->data[0] | ((int)this->data[1] << 8);
            }
            else if (arraySize == 1)
            {
                Int = this->data[0];
            }
            return Int;
        };
};

抛出错误：

Error   LNK2019 unresolved external symbol "public: __thiscall Byte::Byte(void)" (??0Byte@@QAE@XZ) referenced in function "public: static void __cdecl DataParser::Parse(class nlohmann::basic_json<class std::map,class std::vector,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,bool,__int64,unsigned __int64,double,class std::allocator,struct nlohmann::adl_serializer>)" (?ParseToDataTable@Parse@@SAXV?$basic_json@Vmap@std@@Vvector@2@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@2@_N_J_KNVallocator@2@Uadl_serializer@nlohmann@@@nlohmann@@@Z)

我也尝试将其声明为：

const Byte& ToLittleEndianInt(const Byte& s)const {}

那是我在Stephen Prata的C ++ Primer中看到的方式，但是后来我仍然遇到错误，我必须在cpp中像这样使用它：

std::vector<unsigned char> test(3);
for (int i = 0; i < 2; i++)
        test[i] = i;
    Byte CurrentBytes;
    CurrentBytes.data = test;
    CurrentBytes.ColumnWidth=2;
    int results = CurrentBytes.ToLEInt(CurrentBytes);
    //instead of this way which is better
    int results = CurrentBytes.ToLittleEndianInt();

然后我尝试将声明放在类块之外，但随后出现一个错误，提示未定义LEInt，

int Byte::ToLittleEndianInt(){}

当我尝试将int ToLittleEndianInt();添加到公共类块时，它抱怨说它已被定义。添加此内容的正确方法是什么？

更新：

当我将其用作结构时，它会起作用：

struct Byte
{
    std::string  DataType;
    int  ColumnWidth;
    int StartingPosition;
    std::string Column;
    std::vector<unsigned char> data;
    int ToLEInt() {
        long int Int = 0;
        int arraySize = this->ColumnWidth;
        if (arraySize == 2)
        {
            Int = this->data[0] | ((int)this->data[1] << 8);
        }
        else if (arraySize == 1)
        {
            Int = this->data[0];
        }
        return Int;
    };
    std::string ToString()
    {
        int i;
        std::string s = "";
        int arraySize = this->ColumnWidth;
        for (i = 0; i < arraySize; i++) {
            std::string n(1, this->data[i]);
            s = s + n;
        }
        return s;
    }
};

具有扩展方法的自定义类

更新：

0 个答案: